1. Field of the Invention
The present invention relates to a technology for projecting an image.
2. Description of the Related Art
With development in electronic information media, there are more opportunities to use an image projection apparatus (i.e., a projector) including a lighting optical system including a light source and other optical components, a spatial light modulator (SLM) such as a liquid crystal light modulator that modulates a light beam emitted from the lighting optical system based on image information received from an external device, and a projection optical system such as a projection lens to display an image by projecting the light beam modulated by the SLM as an enlarged image on a screen. Particularly, a liquid crystal projector using a liquid crystal light modulator as the SLM is famous among projectors. The liquid crystal projector is capable of easily adjusting a screen size and excellent in color reproduction, which is widely used as, for example, a projector in a conference room.
With the increasing use of the projector, there is a rapidly increasing demand for simplifying a structure and decreasing a size of the projector. To simplify and downsize the projector, downsizing and weight reduction of the projection lens that constitutes the projection optical system has been a key subject. For downsizing and weight reduction of the projection lens, a reduction in the number of lenses constituting the projection lens is effective. However, the reduction in the number of lenses usually leads to degradation in resolution and imaging performance, such as a distortion aberration, a magnification-chromatic aberration, or astigmatism.
For the aberration in the projection optical system, a method has been proposed in which various types of aberrations occurring in the projection optical system are figured out at the time of designing the projection optical system and the shape and the structure of the SLM are adjusted to compensate in advance the aberrations occurring in the projection optical system, which reduces the aberrations in the image projected on the screen. For example, Japanese Patent No. 3264916 discloses a method in which an effective area of the SLM, on which an image is formed, is changed depending on a wavelength to compensate a chromatic aberration. Furthermore, Japanese Patent No. 3357026 discloses an SLM having a structure that is distorted in shape or curved depending on a distortion or a distortion aberration that is caused by a projection optical system.
As explained above, improvements can be made to some extent for the aberrations in the projection optical system by modifying the shape or the structure of the SLM. However, in these methods, the SLM to be used requires a special structure, and it is difficult to sufficiently compensate the degradation in resolution of the projection optical system.